High-precision gas delivery and measurement systems such as mass flow controllers (MFCs) are useful in applications such as semiconductor wafer fabrication and other types of materials processing. In many instances, the accuracy of these gas delivery systems needs to be verified.
Mass flow verifiers (MFVs) may be used to verify the accuracy of an MFC, or other fluid delivery device-under-test (DUT). One type of a mass flow verifier is a rate-of-rise (ROR) flow verifier. A typical ROR flow verifier may include a test chamber volume, a pressure sensor, a temperature sensor, and two isolation valves, one upstream and one downstream. The valves may be closed during idle, and may open when a metrology test run is initiated, allowing flow of gas from the MFC through the flow verifier. Once gas flow has stabilized, the downstream valve may be closed, and as a result the gas pressure may begin to rise in the volume. The pressure sensor may measure the pressure rise. This measurement may be used to calculate the inlet flow rate to the MFV, thereby verifying the gas flow accuracy performance of the DUT.